If the appendix is a relatively useless organ in our bodies then why do we have it? Did the appendix once have a purpose as in the bodies of early man?

– Brent Hannify,
Poway

ANSWER: Someone once said that the only function of the appendix is financial support of the surgical profession. About 7 percent of the population in developed countries will suffer from appendicitis in their lifetime, but appendicitis seems to be rare in undeveloped countries. It is not clear if diet or some other factor contributes to this difference.

In humans, the appendix is a wormlike pouch, 3 1/2 inches long on average, attached to the first part of the large intestine. In herbivorous mammals, such as rabbits, a much larger analogous structure houses bacteria that help break down cellulose, a large plant molecule. The appendix is present in many vertebrates, including other primates.

The human appendix does not contain cellulose-digesting bacteria and humans cannot digest cellulose (which is why lettuce is roughage).

Therefore, the appendix is often called a vestigial organ – a structure that has become diminished in size and lost its original physiological function.

However, that does not mean the human appendix has no function. Of the many functions hypothesized, a role in immunity is considered the most likely, though this remains controversial.

The appendix, along with other parts of the digestive system, produces immune system cells, which can respond to ingested, disease-causing microbes. Whether the appendix contributes significantly to the immune response is not known, since the lack of an appendix does not cause any obvious health problems.

After I wash and dry my car windows on a bright, sunny day, I notice a grid of circles about the size of quarters visible in the glass that wasn't there before I washed them. What is this?

– Ken Garnant,
San Diego

It is mineral deposits, such as calcium and iron, left behind when the water evaporates. The pattern depends on how the water evaporates. (How well water sheets from your car, wind, etc.) Also, the concentration of minerals varies in water from different sources.

Vinegar, a weak acid, can help dissolve the minerals and is supposedly the secret of expert car detailers. However, it will remove your wax and cannot fix the paint if the minerals have etched it. Auto aficionados seeking to prevent mineral deposits can purchase a water deionizer that attaches to a garden hose.

Sherry Seethaler has a doctorate in science education and is a UCSD science writer and educator. Send your scientific questions to her at Quest, San Diego Union-Tribune, P.O. Box 120191, San Diego, CA 92112-0191. Or e-mail sseethaler@ucsd.edu. Please include your name, city of residence and phone number.